Interference suppression methods for 802.11

ABSTRACT

An 802.11 source station transmits a signal with the duration field other than that required for the transmission to prevent transmission by other stations during known sequences. Thus, the source station uses the duration field to spoof the actual time the medium will be occupied, to stations within range of the signal. A station within range of the transmitted signal will check the duration field of the transmitted signal, and update the station&#39;s network allocation vector. Thus, the station will not transmit because the station&#39;s network allocation vector indicates that the medium is in use, even though the station maybe unable to hear the carrier. Accordingly, spoofed stations may, for example, 1) delay transmission until a more critical transmission has completed, 2) allow unknown or foreign protocol to have preferential use of the medium, 3) prevent interference from hidden stations, and 4) allow sharing of the medium by overlapping basic service sets.

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/272,854, filed Mar. 2, 2001, entitled InterferenceSuppression Methods For 802.11, U.S. Provisional Application No.60/274,259, filed Mar. 7, 2001, entitled Interference SuppressionMethods For 802.11, U.S. Provisional Application No. 60/290,789, filedMay 14, 2001, entitled Interference Suppression Methods For 802.11,which are incorporated by reference herein in their entirety.

[0002] This application is a continuation-in-part of U.S. applicationSer. Nos. 10/044,916 and 10/045,071, entitled Interference SuppressionMethods For 802.11, filed on Jan. 15, 2002, and is related to U.S.applications to Interference Suppression Methods For 802.11 which arefiled on even date herewith. These applications are co-pending andcommonly assigned.

BACKGROUND OF THE INVENTION

[0003] Wireless local area networks (WLANs) employ a plurality of mobilenetwork stations, such as data processing devices having wirelesscommunication capabilities. Access to the wireless medium in such anetwork is controlled in each station by a set media access control(MAC) protocol based on a listen-before-talk scheme.

[0004] IEEE 802.11 is a well-established standard for implementing mediaaccess control. An enhanced version of the 802.11 standard is the802.11e standard.

SUMMARY OF THE INVENTION

[0005] In development of quality of service enhancements for theexisting 802.11 standard, it is desirable to guarantee the time a packetor frame will be delivered on the wireless local area networks. However,when new protocols within new versions such as the enhanced 802.11estandard are introduced, there may be stations on the wireless localarea networks that may not understand these new protocols. That is,there may be older stations in the wireless local area network that maynot be equipped to practice the enhanced 802.11e standard. Furthermore,not all new stations practice the enhanced 802.11e standard.Accordingly, the older stations or stations not practicing the enhanced802.11e standard might interfere with the enhanced 802.11e protocols.

[0006] Thus, interference may occur that may prevent reception ofanother desired transmission, or that may cause another transmission tobe delayed, so that the delayed transmission is no longer useful oncereceived.

[0007] In accordance with the various exemplary embodiments of thisinvention, while a first source station is transmitting on a medium,transmission from a second source station that is not equipped topractice the enhanced 802.11e standard, or that does not practice theenhanced 802.11e standard, is prevented from starting while the firstsource station is still using the medium. Thus, in accordance with thevarious exemplary embodiments of this invention, loss of a packet frombeing received by a destination station due to the interference from asecond source station is prevented.

[0008] In accordance with the exemplary embodiments of this invention,virtual carrier detection to determine a medium's availability fortransmission is implemented using the 802.11 frames. In these exemplaryembodiments, using clear channel assessment, the source station desiringto use the medium will not transmit until it determines that the mediumis clear, i.e., when it determines that no carrier or significant signalis present. In accordance with the exemplary embodiments of thisinvention, transmissions earlier in a sequence are provided withinformation concerning the transmissions later in the sequence, wherebyinformation concerning the later transmissions is used to determine themedium's availability.

[0009] In various exemplary embodiments of this invention, an 802.11duration field may be used to indicate periods of time when no carriermay be present, or a non-802.11 carrier may be present on the medium.For example, a source station may use the duration field to indicatetimes where if a transmission is begun from the source station, thesource station may cause delay in another transmission.

[0010] In accordance with these various exemplary embodiments of thisinvention, an 802.11 source station transmits a signal with a durationfield other than that required for the transmission to preventtransmission by other stations during known sequences. In accordancewith these exemplary embodiments, a duration field is used to “spoof”,or misrepresent the actual time the medium will be occupied, to stationswithin range of the signal.

[0011] In accordance with other exemplary embodiments, a specific set of802.11 stations, rather than all stations within range of the signal,are involved in the spoofing scheme. In accordance with other variousexemplary embodiments of this invention, the application of the durationfield may be further generalized to apply to specific sets of stations.By applying group addressing with a duration field, sets of stations aredetermined as to whether the stations should obey the duration field setin the signal. Thus, a specific group of stations could be caused tosuppress transmission.

[0012] In accordance with other exemplary embodiments of this invention,an 802.11 CF-End message may be used to indicate the end of the periodof time for suppressing transmission. For example, a source station mayuse the CF-End message to indicate times where if a transmission fromthe source station has ended as well as after the delay of othertransmissions, the source station may cause transmissions from allstations that had suppressed their transmissions to resume transmittingby resetting a suppression mechanism.

[0013] In accordance with these various exemplary embodiments of thisinvention, an 802.11 source station transmits a CF-End message toindicate the end of the period of time for suppressing transmission fromother stations other than that representing the end of thecontention-free period. That is, in accordance with these exemplaryembodiments, the CF-End message is used to misrepresent to stationswithin range of the signal the actual reset time for resetting thenetwork allocation vectors (NAV).

[0014] In accordance with other various exemplary embodiments, groupaddressing is provided that only stations in a particular group arecaused to reset their suppression mechanism.

[0015] In accordance with the various exemplary embodiments of thisinvention, a station within range of the transmitted signal will checkthe duration field and the CF-End message of the transmitted signal, andset or reset the station's network allocation vector (NAV). Thus, aspoofed station will not transmit because the station's networkallocation vector indicates that the medium is in use, even though thestation maybe unable to hear the carrier.

[0016] In accordance with the various exemplary embodiments of thisinvention, because their network allocation vectors indicate that themedium is in use, stations within range of the spoofed signal, includinghidden stations, will be spoofed into suppression, thereby notinterfering with unknown or foreign protocols. That is, in accordancewith these embodiments, spoofed stations may, for example, 1) delaytransmission until a more critical transmission has completed, 2) allowunknown or foreign protocol to have preferential use of the medium, 3)prevent interference from hidden stations, and 4) allow sharing of themedium by overlapping basic service sets.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 shows an exemplary embodiment of a wireless local areanetwork.

[0018]FIG. 2 shows an exemplary embodiment of a station in the wirelesslocal area network.

[0019]FIG. 3 shows detailed operation of the method to exchange controlinformation when transmitting data from a transmitting station to areceiving station.

[0020]FIG. 4 shows an exemplary embodiment of the request-to-send (RTS)frame format.

[0021]FIG. 5 shows an exemplary embodiment of the clear-to-send (CTS)frame format.

[0022]FIG. 6 shows one exemplary method of enhancing the signaltransmission according to this invention.

[0023]FIG. 7 shows another exemplary method of enhancing the signaltransmission according to this invention.

[0024]FIG. 8 is a flowchart illustrating an exemplary method ofenhancing the signal transmission according to this invention.

[0025]FIG. 9 is a flowchart illustrating another exemplary method ofenhancing the signal transmission according to this invention.

[0026]FIG. 10 is a flowchart illustrating another exemplary method ofenhancing the signal transmission according to this invention.

[0027]FIG. 11 is a flowchart illustrating another exemplary method ofenhancing the signal transmission according to this invention.

DETAILED DESCRIPTION

[0028]FIG. 1 discloses an exemplary embodiment of a wireless local areanetwork (WLAN). It should be appreciated that various types of localarea networks for forwarding messages to and receiving messages fromnetwork stations may be employed in the various exemplary embodiments ofthis invention.

[0029] As shown in FIG. 1, the wireless local area network 10 includes adistribution system 100, stations 160-1 and 160-2 provided in a firstbasic service set BSS1 having the same basic service, and stations 160-3and 160-4 provided in a second basic service set BSS2 having the samebasic service. For example, stations 160-1 and 160-2 are networkstations provided within a cell under a common coordinating function,with one of the stations providing access to the distribution system 100being an access point (AP) to a basic service set. Similarly, stations160-3 and 160-4 are network stations provided within a cell under acommon coordinating function, with one of the stations providing accessto the distribution system 100 being an access point (AP) to a secondbasic service set. Stations 160-1 to 160-4 together with thedistribution system 100 form an extended service set (ESS), where allstations may communicate with each other without involving entitiesoutside of the 802.11 media access control (MAC) architecture. It shouldbe appreciated that any of the stations 160-1 to 160-4 that are notaccess points may also be mobile network stations.

[0030] Further, it should be appreciated that the stations 160-1, 160-2,160-3 and 160-4 may be connected to other devices and/or networks withwhich the stations may communicate. Furthermore, though FIG. 1 onlyshows four stations within the wireless local area network 10, it shouldbe appreciated that a wireless local area network may include more thanfour stations. That is, it should be appreciated that the basic servicesets BSS1 and BSS2 may each include more than two stations in accordancewith this invention.

[0031] As shown in FIG. 1, stations 160-2 and 160-3 are also accesspoints (AP) that provide access to the distribution system 100 by thebasic service sets BSS1 and BSS2, respectively. The distribution system100 enables mobile network station support to the mobile networkstations 160-1 and 160-4 by providing the logical services necessary tohandle address to destination mapping and seamless integration ofmultiple basic service sets. Data moves between the basic service setsBSS1 and BSS2 and the distribution system 100 via access points. Inaccordance with these exemplary embodiments, because the access pointsare also stations 160-2 and 160-3, they are addressable entities. Itshould be appreciated that though FIG. 1 shows basic service sets BSS1and BSS2 as two separate sets, in accordance with various exemplaryembodiment of this invention, the basic service sets may partiallyoverlap, be physically disjointed, or be physically collocated.

[0032] As shown in FIG. 1, to send a data message from station 160-1 tostation 160-4, for example, the message is sent from station 160-1 tostation 160-2, which is the input access point for basic service setBSS1 to the distribution system 100. Station 160-2, as an access point,gives the message to the distribution service of the distribution system100. The distribution service delivers the message within thedistribution system 100 in such a way that the message arrives at theappropriate distribution system destination for the intended station,station 160-4. In the exemplary embodiment of FIG. 1, the message isdistributed by the distribution service to station 160-3, which is theoutput access point for basic service set BSS2, and station 160-3accesses a wireless medium to send the message to the intendeddestination, station 160-4.

[0033]FIG. 2 discloses an exemplary embodiment of a station in thewireless local area network, such as a mobile network station. As shownin FIG. 2, a station 200 is provided with an antenna 220, a receivingunit 240, a transmitting unit 260, and a central processing unit (CPU)280. The mobile network station 200 selectively transmits and receivesmessages.

[0034] When receiving data, a signal received by the mobile networkstation 200 is received by the antenna 220, demodulated into controlinformation or data through the receiving unit 240. Based on the controlinformation addressed at the receiving unit 240, the central processingunit (CPU) 280 controls receipt of data by the receiving unit 240.

[0035] In transmitting data, the central processing unit (CPU) 280identifies whether or not the medium is unused for a time period. If thecentral processing unit (CPU) 280 determines that the medium is busy,the central processing unit (CPU) 280 proceeds to defer mode, while ifthe central processing unit (CPU) 280 detects that the medium is unusedfor an appropriate period of time, the transmitting unit 260 transmitsdata.

[0036]FIG. 3 shows detailed operation of the method to exchange controlinformation when transmitting data from a transmitting station to areceiving station, according to an exemplary embodiment of thisinvention. As shown in FIG. 3, a request-to-send signal (RTS) 81 is usedby a transmitting station as control information for identifying themedium connectability to a receiving station. A clear-to-send signal(CTS) 82 is used by the receiving station as control information forresponding to the identification made by the request-to-send signal(RTS) 81. Data 83 is sent by the transmitting station after theclear-to-send signal (CTS) 82 has been sent. An acknowledgment signal(Ack) 84 is used by the receiving station as control information foracknowledging the data reception of data 83. Subsequent data issubjected to a succeeding procedure started by another station afterconfirming termination of the transmission procedure between thetransmitting and receiving stations, as acknowledged by theacknowledgment signal (Ack) 84 from the receiving station.

[0037] As shown in FIG. 3, time intervals such as inter-frame spaces(IFS) are provided between frames. A station determines that the mediumis idle through the use of the virtual carrier detection to determine amedium's availability for transmission for the interval specified. Asshown in FIG. 3, the inter-frame spaces (IFS) may include shortinter-frame spaces (SIFS), PCF inter-frame spaces (PIFS), and DCFinter-frame spaces (DIFS).

[0038] As shown in FIG. 3, short inter-frame spaces (SIFS) are used asgaps between exchange procedures. For example, as shown in FIG. 3, theshort inter-frame spaces (SIFS) 816, 812, and 813 are used respectivelyas gaps between the request-to-send (RTS) frame 81, the clear-to-send(CTS) frame 82, the data frame 83, and the acknowledgment (Ack) frame84, for example. A short inter-frame space (SIFS) indicates the timefrom the end of the last symbol of the previous frame to the beginningof the first symbol of the preamble of the subsequent frame as seen atthe air interface. The short inter-frame space (SIFS) is the shortest ofthe inter-frame spaces and is used when stations have seized the mediumand need to keep the medium for the duration of the frame exchangesequence to be performed. Using the smallest gap between transmissionswithin the frame exchange sequence prevents other stations, which arerequired to wait for the medium to be idle for a longer gap, fromattempting to use the medium, thus giving priority to completion of theframe exchange sequence in progress.

[0039] As shown in FIG. 3, DCF inter-frame spaces (DIFS) are used bystations operation under the distributed coordination function (DCF) totransmit data frames and management frames. A station using thedistributed coordination function (DCF) transmits a data frame if thevirtual carrier detection mechanism determines that the medium is idle.As shown in FIG. 3, at a starting point of the exchange procedure from atransmitting station to a receiving station, DCF inter-frame space(DIFS) 811 is spent for confirming connectability (channel occupationstatus) on the medium for transmission of the request-to-send signal(RTS) 81. Further, as shown in FIG. 3, after data 83 has been delivered,supplemental DCF inter-frame space (DIFS) 814 is spent, and the stationperforms a backoff procedure.

[0040] A data frame format comprises a set of fields that occur in afixed order in all frames. These fields are used to indicate theidentification of the basic service set, the address of the sourcestation, the address of the destination station, the address of thetransmitting station and the address of the receiving station, forexample. FIGS. 4 and 5 show exemplary embodiments of the frame formatsaccording to this invention.

[0041]FIG. 4 shows an exemplary embodiment of the request-to-send (RTS)frame format. As shown in FIG. 4, the request-to-send (RTS) frame 400includes a frame control field 410 for frame control, a duration field420 for the duration, a receiving station address field 430 for theaddress of the receiving station, a transmitting station address field440 for the address of the transmitting station, and a frame checksequence field 450 as a calculation field for a parity check. In therequest-to-send frame format of FIG. 4, the receiving station address isthe address of the station that is the intended immediate recipient ofthe pending directed data or management frame. The transmitting stationaddress is the address of the station transmitting the request-to-send(RTS) frame 400.

[0042]FIG. 5 shows an exemplary embodiment of the clear-to-send (CTS)frame format. As shown in FIG. 5, the clear-to-send (CTS) frame 500includes a frame control field 510, a duration field 520, a receivingstation address field 530, and a frame check sequence field 550. In theclear-to-send (CTS) frame format of FIG. 5, the receiving stationaddress is the address copied from the transmitting station field 440 ofthe immediately previous request-to-send (RTS) frame 400 to which theclear-to-send (CTS) frame 500 is a response.

[0043] For a station to transmit, using virtual and physical carrierdetection, the station determines if another station is transmitting. Ifno station is determined to be transmitting, the transmission mayproceed. The transmitting station ensures that no other station istransmitting for a required duration before attempting to transmit. Ifanother station is determined to be transmitting, the detecting stationdefers transmission until the end of the current transmission.

[0044] The request-to-send (RTS) and the clear-to-send (CTS) frames 400and 500 are exchanged prior to the actual data frame to distributemedium reservation information to announce the impending use of themedium. In accordance with an exemplary embodiment, the request-to-send(RTS) and the clear-to-send (CTS) frames 400 and 500 contain a durationfield that defines the period of time that the medium is to be reservedto transmit the actual data frame and the returning acknowledgmentframe. All stations within the reception range of either the originatingstation which transmits the request-to-send (RTS) signal or thedestination station which transmits the clear-to-send (CTS) frame learnsof the medium reservation. Thus, a station can be unable to receive fromthe originating station yet still know about the impending use of themedium to transmit a data frame.

[0045] The request-to-send (RTS) and clear-to-send (CTS) signals 81 and82 contain information to set the network allocation vectors (NAV) forthe stations within the range of the signals. In FIG. 3, each networkallocation vector (NAV) field 821 in 822 shows the information containedin the request-to-send (RTS) and clear-to-send (CTS) signals 81 and 82,respectively.

[0046] The network allocation vector (NAV) maintains a prediction offuture traffic on the medium based on duration information that isannounced in the request-to-send (RTS) and clear-to-send (CTS) frames 81and 82 prior to the actual exchange of data.

[0047] A station receiving a valid frame updates the station's networkallocation vector (NAV) with the information received in the durationfield contained in frame. As shown in FIG. 3, stations receiving therequest-to-send (RTS) frame 81 set the network allocation vector (NAV)821 in accordance with the request-to-send (RTS) frame 81, whilestations only receiving the clear-to-send (CTS) frame 82 set theirnetwork allocation vector (NAV) 822 in accordance with the clear-to-send(CTS) frame 82, resulting in the lower network allocation vector (NAV)as shown in FIG. 3.

[0048] At the nominal beginning of each contention free period (CFP),the access point (AP) senses the medium. When the medium is determinedto be idle for a period of time, the access point (AP) transmits abeacon frame. After the initial beacon frame, the access point (AP)waits for at least another period of time, and then transmits one of 1)a data frame, 2) a CF-Poll frame with which the access point (AP)requests one of the stations to transfer a data packet, 3) aData+CF-Poll frame which contains a poll and data for the polledstation, or 4) a CF-End frame which indicates the end of the contentionfree period (CFP).

[0049] In the exemplary embodiment in FIG. 3, at a starting point of theexchange procedure from a transmitting station to a receiving station,DCF inter-frame spaces (DIFS) 811 and 814 are spent in the contentionperiod (CP) for confirming connectability (channel occupation status) onthe medium for transmission of the request-to-send signal (RTS) 81. Inaccordance with other various exemplary embodiments of this invention,to confirm connectability on the medium for transmission of therequest-to-send signal (RTS) 81, shorter PCF inter-frame spaces (PIFS)may be used instead of the DCF inter-frame spaces (DIFS) 811 and 814with the request-to-send signal (RTS) transmission. Thus, by using thePCF inter-frame spaces (PIFS), priority access to the medium may beobtained.

[0050] Though the shorter PCF inter-frame spaces (PIFS) are not normallyused outside of the 802.11 contention free period (CFP) and arequest-to-send signal (RTS) is normally only transmitted in thecontention period (CP), in these exemplary embodiments, arequest-to-send signal (RTS) could be used in the contention free period(CFP) or a PCF inter-frame spaces (PIFS) could be used in the contentionperiod (CP) so as to prevent various stations from transmitting atinappropriate times. In these embodiments, receiving stations wouldbehave in a predictable manner and would be suppressed, potentiallyreducing the possibility of interference.

[0051] Transmission of a frame from station 160-1 to station 160-2 ofFIG. 1, for example, may not be heard by another station wishing to usethe medium to transmit subsequent data because the another station maybe too far away, or there may be intervening obstacles. In addition,transmission of the subsequent data may interfere with the transmissionof data 83 if the another station transmitting the subsequent data doesnot understand the protocol of station 160-1 transmitting data 83.Without enhancements, the another station may start to transmit thesubsequent data while the first station, station 160-1, is still usingthe medium. Accordingly, the receiving station for data 83, station160-2, for example, may hear both transmitting stations 160-1 and theanother station transmitting the subsequent data, and the data 83 beingreceived will be lost due to the transmission of the subsequent datafrom the second transmitting station.

[0052] As discussed above, in accordance with exemplary embodiments ofthis invention, the request-to-send (RTS) and clear-to-send (CTS)signals 81 and 82 include information which indicates the availabilityof the medium for the subsequent transmission of the subsequent data.For example, request-to-send (RTS) and clear-to-send (CTS) signals 81and 82 may include a duration value in the duration field to indicatemedium availability. A station within the range of the signal will checkthe duration field of the signal, and update the station's networkallocation vector (NAV) to indicate when the medium is known in advanceto be busy. Then, even if no carrier is sensed on the medium, thestation will not transmit as it knows the medium is in use, even thoughit maybe unable to hear the carrier. That is, in these exemplaryembodiments of this invention, the 802.11 duration field is used toindicate periods of time when no carrier may be present, or a non-802.11carrier may be present, and the duration field is used to suppresstransmissions from stations so as to avoid interference from thesuppressed stations.

[0053]FIG. 6 shows one exemplary method of enhancing the signaltransmission according to this invention. In this embodiment, theduration field set to a predetermined value other than the duration timefor the subsequent transmissions is sent by a transmitting station, andthe stations within the range of the sent signal will update theirnetwork allocation vector (NAV) in accordance with the set durationfield value.

[0054] As shown in FIG. 6, the network allocation vector (NAV) for thestations within the range of the transmitted signal 80, such as aclear-to-send signal (CTS) or request-to-send signal (RTS), is set to begreater than the time required for subsequent transmissions Tx1, Tx2, .. . TxN by the stations within the range. Because the stations withinthe range and obeying the duration field may believe the duration fieldrepresents the time it will take for transmissions immediately followingthe sequence, the obeying stations are in essence being spoofed by thetransmitting station. That is, the duration field is not being used bythe transmitting station for its intended purpose of representing thetime it will take for transmissions immediately following the sequence.Rather, the duration field is used by the transmitting station toindicate times to suppress the transmissions Tx1, Tx2, . . . TxN by thestations within the range of the signal 80, where if the suppressedtransmissions Tx1, Tx2, . . . TxN have begun, another more criticaltransmission may be delayed, a protocol other than 802.11 which might beundetectable to the 802.11 station may interfere with the 802.11station, or the transmitting 802.11 stations may interfere with aforeign protocol or advanced 802.11 protocol. Thus, in FIG. 6, duringthe suppressed time period set by the network allocation vector (NAV),transmissions, Tx1, Tx2 . . . TxN from the stations obeying the durationfield are suppressed. By spoofing to the stations obeying the durationfield, it is possible to get the obeying stations to exhibit behaviorfor which it was not originally programmed, such as delaying thetransmissions Tx1, Tx2, . . . TxN until a more critical transmission hascompleted or suppressing transmission so that undetectable protocols maynot interfere.

[0055] In the network of FIG. 1, if station 160-2 wishes to preventanother station from causing a beacon from being transmitted beyond thetarget beacon transmit time (TBTT), for example, station 160-2 may senda signal to another station such as station 160-1 containing a durationtime that exceeds the normal requirements of the protocol so as to coverany time remaining between the current time, and the next target beacontransmit time. Station 160-1 and other stations within range of the sentsignal will not realize that the duration field is incorrectly set, andmight even propagate the signal further by re-transmitting the durationfield. Thus, in this example, station 160-2 would send a signal, such asa request-to-send signal (RTS), to station 160-1 with the duration fieldset to cover the remaining time to the target beacon transmit time, andthe receiving station 160-1 would respond with a clear-to-send signal(CTS) whose duration would be set to cover the remaining time to thetarget beacon transmit time as well. All stations within range of therequest-to-send signal (RTS), clear-to-send signal (CTS), or both wouldset their network allocation vectors (NAV) so as not to attempttransmission again until after the target beacon transmit time.

[0056] In accordance with other exemplary embodiments of this invention,the application of the duration field may be further generalized toapply to specific sets of stations rather than all stations withinrange. That is, in accordance with these exemplary embodiment, onlyspecific sets of stations are spoofed by the duration field. Forexample, enhanced stations under the 802.11e or later standard couldapply group addressing with the duration field to determine which setsof stations should obey the duration field, and which should ignore it.Thus, a specific group of stations, such as legacy stations which do notapply the enhanced 802.11e standard, could be caused to suppresstransmission. That is, because stations applying the enhanced 802.11estandards may already contain protocols that prevent them fromtransmitting at a suppressed time and the legacy stations which do notapply the enhanced 802.11e standards do not contain these protocols,these legacy stations may be treated as a special group. In this case,the transmitting station sends the signal only to the group of legacystations.

[0057] A transmitting station wishing to block usage of the medium by aset of stations sets the duration field for the length of time duringwhich usage of the medium is to be restricted. Other parameters in thetransmission determine which specific group of stations should recognizethe value of the duration field. Stations not in this specific groupwould ignore the value of the duration field. Thus, in the example ofFIG. 6, if the transmitting station wishes to block usage of the mediumby a group of legacy stations, suppressed transmissions Tx1, Tx2 . . .TxN within the time period set by the network allocation vector (NAV)would only be transmissions from legacy stations.

[0058] In an exemplary embodiment, a transmitting station such as anaccess port (AP) may send a signal, such as the clear-to-send signal(CTS), to a group address. In group addressing, the station transmittingto the group address has access to lists of assigned group addresses andthe properties for membership in each of these addresses. A stationwithin range of the clear-to-send (CTS) signal may identify if thereceiving station address (RA) of the sent signal is a group address andwhether or not the station belongs to that group. A specific set ofstations, such as the stations applying an enhanced 802.11e standard,would ignore the duration field of the clear-to-send signal (CTS) if thereceiving station address (RA) in a clear-to-send signal (CTS) were setto the group address. The specific set of stations would then surmisethat the transmitting station was spoofing the stations that are notapplying the enhanced 802.11 standards, such as legacy stations. Thestations applying the enhanced 802.11 standards would ignore theduration field in the clear-to-send signal clear-to-send (CTS), andstill would be free to transmit. Since stations applying the enhanced802.11 standards in accordance with this invention know not to delay thebeacon from the transmitting access port (AP), the stations applying theenhanced 802.11 standards are free to use the medium. On the other hand,legacy stations and other stations which do not apply the enhanced802.11 standards would not detect that they are being spoofed, and wouldset their network allocation vectors for the duration value in theclear-to-send signal (CTS) so as not to transmit. Thus, the spoofedstations are prevented from transmitting at the target beacon transmittime and delaying the beacon from the transmitting access point (AP).

[0059] Table 1 shows an exemplary embodiment of the effects of aclear-to-send (CTS) signal on stations within range of the signal. Itshould be appreciated that since a legacy station (LSTA) will always setits network allocation vector (NAV) according to the received signal,effects on legacy stations are not shown in Table 1. TABLE 1 Message RAEffect CTS STA Set NAV CTS group Set NAV if not in Group CTS broadcastSet if legacy station

[0060] As shown in Table 1, when a clear-to-send (CTS) signal istransmitted, if a station (STA) identifies that the receiving stationaddress (RA) in the clear-to-send (CTS) signal is the station's ownaddress, that is, a unicast address, the station will set the station'snetwork allocation vector (NAV) in accordance with the receivedclear-to-send (CTS) signal. If the station identifies that the receivingstation address (RA) of the clear-to-send (CTS) signal is that of agroup address, that is, a multicast address, the station will set thenetwork allocation vector (NAV) if the station is not in the addressedgroup. Alternatively, the protocol may be defined such the station setsits network allocation vector (NAV) if the station is a member of themulticast address. If the receiving station address (RA) of theclear-to-send (CTS) signal is a broadcast address, the station will setit network allocation vector (NAV) only if it is a legacy station thatdoes not practice the enhanced 802.11e standard.

[0061] It should be appreciated that, while a station transmitting aclear-to-send signal (CTS) may usually expect signals sent in response,in accordance with the various exemplary embodiments of this invention,the clear-to-send signal (CTS) is merely sent for setting the networkallocation vector (NAV), and thus, no other responses are expected bythe station transmitting a clear-to-send signal (CTS). It should beappreciated that similar provisions with, for example, 802.11 data ornull frame, that is a data frame containing no data, may be applied inaccordance to this invention.

[0062] In accordance with other exemplary embodiments of this invention,a requirement for resetting network allocation vectors when aclear-to-send (CTS) signal is not detected after a request-to-send (RTS)signal, or when no frame is detected within a predetermined time periodof a request-to send (RTS) signal, is added. In an example, if some ofthe stations in a basic service set (BSS) are legacy stations whichrequire resetting the network allocation vectors when a clear-to-send(CTS) signal is not detected, an additional message such as anadditional clear-to-send (CTS) signal may be sent to the broadcastaddress or to the sender's own address. This additional clear-to-send(CTS) signal or any other similarly encoded frame may be transmittedimmediately after the first clear-to-send (CTS) signal response to therequest-to-send (RTS) signal, or otherwise may immediately follow therequest-to-send (RTS) signal. A station not hindered by thisrequirement, such as stations practicing enhanced 802.11e standards, maynot be affected by the additional clear-to-send (CTS) signal, since theadditional clear-to-send (CTS) signal contains a duration valuecorresponding to the same network time for resetting of the networkallocation vector (NAV) as the prior request-to-send (RTS) andclear-to-send (CTS) signals. The stations receiving the additionalclear-to-send (CTS) signal may defer resetting their network allocationvectors until the desired duration had expired.

[0063] Accordingly, in protocol sharing, for example, by having thestation that sends the request-to-send signal (RTS) also send theadditional clear-to-send signal (CTS), stations which have problems inhearing the first clear-to-send signal (CTS) may be prevented fromincorrectly resetting the network allocation vector (NAV). Thus, thesetting of the network allocation vector (NAV) to that of therequest-to-send signal (RTS) may be guaranteed, and the medium may bereserved appropriately.

[0064] It should be appreciated that this invention is not limited tosending of an additional clear-to-send (CTS) signal after the firstclear-to-send (CTS) signal, and that other message types such as a null,acknowledgement signal or data frames could be used to perform the samefunction as the clear-to-send (CTS) signal.

[0065] Table 2 shows an exemplary embodiment of the effects of arequest-to-send (RTS) signal on stations within range of the signal. Itshould be appreciated that other similar encodings may be developed bythose skilled in the art using the principles disclosed in thisinvention. As in Table 1, since a legacy station will always set itsnetwork allocation vector (NAV) according to the received signal,effects on legacy station are not shown in Table 2. TABLE 2 Message TARA Effect RTS unicast1 unicast1 Set NAV if not in same BSS RTS unicast1unicast2 Set NAV, Respond CTS, Obey NAV for CTS RTS unicast1 multicast1Set NAV if not in Group RTS unicast1 broadcast Set NAV RTS multicast1unicast1 Set NAV if not in Group, send CTS to Group, ignore NAV for CTS,obey physical CCA RTS multicast1 multicast1 Set NAV if not in Group,send CTS to Group, ignore NAV for CTS, obey physical CCA RTS multicast1multicast2 Set NAV if not in Group, send CTS to Group 1, ignore NAV forCTS, obey physical CCA RTS multicast1 broadcast Set NAV RTS broadcastunicast1 Set NAV if not in same BSS RTS broadcast multicast1 Set NAV ifnot in same Group RTS broadcast broadcast Set NAV

[0066] As shown in Table 2, when a request-to-send (RTS) signal istransmitted, a station identifies the transmitting station address (TA)and the receiving station address (RA) in the request-to-send (RTS)signal, and sets the station's network allocation vector (NAV)accordingly. As shown in Table 2, if the transmitting station address(TA) is of a first unicast address (unicast1), the station will set itsnetwork allocation vector (NAV) if 1) the receiving station address (RA)is a broadcast address, 2) the receiving station address (RA) is also ofthe first unicast address (unicast1) and the station is in the samebasic service set as the first unicast address (unicast1), or 3) if thereceiving station address (RA) is a multicast address (multicast1) andthe station is not in the same group as the addressed group. Further, ifthe receiving station address is another unicast address (unicast2), thestation will set its network allocation vector (NAV) accordingly,respond with a clear-to-send (CTS) signal if the station's address isthe another unicast address (unicast2), and obey the network allocationvector (NAV) in the clear-to-send (CTS) signal.

[0067] As shown in Table 2, if the transmitting station address (TA) isof a first multicast address (multicast1), the station will set itsnetwork allocation vector (NAV) if the receiving station address (RA) isa broadcast address. Further, if the receiving station address (RA) isalso of the first multicast address (multicast1) or another multicastaddress (multicast2), or a unicast address (unicast1), the station willset its network allocation vector (NAV) accordingly if the station isnot in the addressed group of the first multicast address (multicast1),respond with a clear-to-send (CTS) signal if addressed by the receivingstation address (RA), ignore the network allocation vector (NAV) fortransmitting the clear-to-send (CTS) signal, but obey physical clearchannel assessment (CCA). It should be appreciated that it is alsopossible to encode the message such that the network allocation vector(NAV) is set if the station is in the addressed group of the firstmulticast (multicast1).

[0068] Further, as shown in Table 2, if the transmitting station address(TA) is of a broadcast address (Broadcast), the station will set itsnetwork allocation vector (NAV) if 1) the receiving station address (RA)is a broadcast address, 2) the receiving station address (RA) is also ofthe first unicast address (unicast1) and the station is in the samebasic service set as the first unicast address (unicast1), or 3) if thereceiving station address (RA) is a multicast address (multicast1) andthe station is not in the same group as the addressed group.

[0069] It should be appreciated that the use of the techniques of thisinvention could be for sharing with a non-802.11 protocol. If the mediumis to be reserved for a period of time for use by a non-802.11 protocol,the transmitting station could send a message with the duration fieldset so as to prevent use of the medium by 802.11 stations when anotherprotocol is active. For example, as shown in FIG. 7, a stationpracticing the enhanced 802.11e standards could send a signal 80, suchas a clear-to-send signal (CTS), to itself with a duration field set toa specified duration value. All stations including stations practicingthe enhanced 802.11e standards would set their network allocationvectors (NAV) accordingly. The other unknown or foreign protocol wouldthen have preferential use of the medium during that specified durationvalue interval. The stations practicing the 802.11 standards within therange of the clear-to-send signal (CTS) would set their networkallocation vectors so as not to use the medium, even thought they mightnot be able to detect the other protocol.

[0070] It should be appreciated that, in accordance with this invention,a station practicing an 802.11e standard or some future enhanced 802.11version may introduce a new protocol within the standard. For example, atoken passing scheme may be introduced within the 802.11e enhancedstandard, or an unscheduled contention free period (CFP) may beintroduced between a transmitting station, such as the access point(AP), and a subset of stations. In accordance with various exemplaryembodiments of this invention, the new protocol is specific to a groupof stations, and stations that are not in the specific group are set tosuppress transmissions. In these exemplary embodiments, the transmittingstation may send a request-to-send signal (RTS) from itself, forexample, to the group's multicast address in which the duration timewould be set for a specific extended period of time. Stations not in thegroup are set to suppress transmissions, while the transmitting stationimplements a protocol of its choosing.

[0071] In other exemplary embodiments of this invention, an 802.11CF-End message may be used to indicate the end of the period of time forsuppressing transmission other than the time indicated by the durationvalue. That is, though the CF-End message is normally only used in the802.11 standards to indicate the end of the contention free period(CFP), in accordance with these embodiments, the CF-End message may beused for other purposes. For example, a source station may use theCF-End message to indicate times where if a transmission from the sourcestation has ended and no further delay of other transmissions isrequired, the source station may cause transmissions from all stationsthat had suppressed their transmissions to resume transmitting byresetting a suppression mechanism.

[0072] In accordance with the various exemplary embodiments of thisinvention, the 802.11 source station transmits a CF-End message at timesother than the times indicating expiration of the contention free period(CFP), to prevent transmission by other stations during known sequences.That is, in accordance with these exemplary embodiments, the CF-Endmessage is also used to spoof stations within range of the signal bylying about the ending of the contention free period (CFP). A stationwithin range of the CF-End signal will update the station's networkallocation vector (NAV) to indicated the reset time of the networkallocation vector (NAV).

[0073] Thus, if a transmitting station decides that it no longer needsthe additional time set aside by the duration field in therequest-to-send signal (RTS), for example, the transmitting station maysend a CF-End to the broadcast address. The CF-End would cause allstations within the range of the CF-End signal to reset the stations'network allocation vectors so as to shorten the time set aside from thatoriginally specified in the duration field. Similarly, if the previoustransmission has ended but the network allocation vector (NAV) has notindicated the end of the suppression duration, as set by the CF-Endsignal, the station will not transmit because the station's networkallocation vector indicates that the medium is still in use.

[0074] It should be appreciated that the application of the enhancedCF-End also can be extended to group addressing so that only stations ina particular group are caused to reset their suppression mechanism.

[0075] Table 3 shows an exemplary embodiment of the effects of a CF-Endsignal on stations within range of the signal. As in Table 1 and Table2, since a legacy station will always set its network allocation vector(NAV) according to the received signal, effects on legacy station arenot shown in Table 3. TABLE 3 Message TA RA Effect CF-End unicast1unicast1 Reset NAV if in same BSS CF-End unicast1 unicast2 Reset NAV ifunicast2 CF-End unicast1 multicast1 Reset NAV if in Group CF-Endunicast1 broadcast Reset NAV CF-End multicast1 unicast1 Reset NAV if inGroup CF-End multicast1 multicast1 Reset NAV if in Group CF-Endmulticast1 multicast2 Reset NAV if in Group 2 CF-End multicast1broadcast Reset NAV CF-End broadcast unicast1 Reset NAV if not in sameBSS CF-End broadcast multicast1 Reset NAV if not in same Group CF-Endbroadcast broadcast Reset NAV

[0076] As shown in Table 3, when a CF-End signal is transmitted, astation identifies the transmitting station address (TA) and thereceiving station address (RA) in the CF-End signal, and sets thestation's network allocation vector (NAV) accordingly. As shown in Table3, if the transmitting station address (TA) is of a first unicastaddress (unicast1), the station resets its network allocation vector(NAV) if 1) the receiving station address (RA) is a broadcast address,2) the receiving station address (RA) is also of the first unicastaddress (unicast1) and the station is in the same basic service set asthe first unicast address (unicast1), or 3) if the receiving stationaddress (RA) is a multicast address (multicast1) and the station is inthe same group as the addressed group. Further, if the receiving stationaddress is another unicast address (unicast2), the station resets itsnetwork allocation vector (NAV) accordingly if the address of thestation is the second unicast address (unicast2).

[0077] As shown in Table 3, if the transmitting station address (TA) isof a first multicast address (multicast1), the station resets itsnetwork allocation vector (NAV) if 1) the receiving station address (RA)is a broadcast address, 2) the receiving station address (RA) is also ofthe first unicast address (unicast1) and the station is in the samegroup as the addressed group, or 3) if the receiving station address(RA) is also the first multicast address (multicast1) and the station isin the same group as the addressed group. Further, if the receivingstation address is another multicast address (multicast2), the stationresets its network allocation vector (NAV) accordingly if the station isin the second group.

[0078] As shown in Table 3, if the transmitting station address (TA) isof a broadcast address (Broadcast), the station resets its networkallocation vector (NAV) if 1) the receiving station address (RA) is abroadcast address, 2) the receiving station address (RA) is also of thefirst unicast address (unicast1) and the station is not in the samebasic service set as the first unicast address (unicast1), or 3) if thereceiving station address (RA) is a multicast address (multicast1) andthe station is not in the same group as the addressed group.

[0079] It should be appreciated that the methods of this invention maybe applied in overlap mitigation of basic service sets (BSS). That is,the methods may be applied when two or more 802.11 basic service sets(BSS) operate in the same area. In such cases, in accordance to variousexemplary embodiments of this invention, the transmitting stations treateach other as foreign protocols, and suppress transmissions within theirown basic service sets (BSS) at scheduled times as discussed above.Thus, in the example shown in FIG. 6, the suppressed transmissions Tx1,Tx2, . . . TxN are thus transmissions within each basic service set(BSS). In these embodiments, the basic service sets (BSS) may take turnssharing the medium.

[0080] In an exemplary embodiment, the station groups are defined as allstations existing in a basic service set that interfere with other basicservice sets. In this exemplary embodiment, group addresses are assignedcorresponding to each of the groups. When a first basic service set anda second basic service set of a plurality of basic service sets arrangea time such that the first basic service set is to suppress interferingtransmissions, the transmitting station for the first basic service setmay issue a signal such as a clear-to-send (CTS) signal to the groupdefined as interfering with the second basic service set. Thus, theimpact to the first basic service set is minimized, as only stationsinterfering with the second basic service set are suppressed.

[0081] It should be appreciated that the network allocation vector (NAV)for a given station may continually be set, due to suppression for theContention Free Period (CFP) from several surrounding basic service sets(BSS). Accordingly, the continually set station may never have thechance to transmit.

[0082] In accordance with other various exemplary embodiments of thisinvention, a suppressed station may send a signal, such as aclear-to-send (CTS) signal, in response to a request-to-send (RTS)signal from the access point (AP) of the suppressed station's own basicservice set (BSS), to the stations addressed from one of the groupssuppressing it. That is, the suppressed station would send aclear-to-send signal (CTS) to the group indicated by the transmittingstation, ignoring the suppressed station's own network allocation vector(NAV). The suppressed station would first wait for the medium to bephysically clear of any messages using physical carrier sense on themedium. When the access point (AP) from the suppressed station's ownbasic service set (BSS) hears the clear-to-send (CTS) signal from thesuppressed station, the access point (AP) would then know that one setof interfering stations were suppressed. The access point (AP) thensends a CF-End message from itself, to the suppressed station. Thiswould clear the suppressed station's network allocation vector (NAV),and allow the cleared station to transmit for some period of time. Thetransmitting station may repeat this process with several groups ofinterfering stations in a row if necessary until the cleared stationscould transmit in a clear medium.

[0083] In essence, in accordance with the various exemplary embodimentsof the present invention, the use of signals such as the request-to-sendsignal (RTS), the clear-to-send signal (CTS), and CF-End would create anunscheduled contention free period (CFP), that could be used toimplement the normal contention free period (CFP) protocol, or anotherprotocol that might be of use in future versions of the 802.11 standard.

[0084] It should be appreciated that enhanced stations according tovarious exemplary embodiments of this invention may be sensitive to whya network allocation vector (NAV) is set. If, for example, the enhancedstation could differentiate between the network allocation vector (NAV)being set because it was in a contention free period (CFP) or being setby a recently transmitted message frame such as data, request-to-sendsignal request-to-send (RTS), or clear-to-send signal (CTS), forexample, it may chose to ignore the network allocation vector (NAV) onlyfor the contention free period (CFP), and obey the network allocationvector (NAV) if it would interrupt an ongoing 802.11 frame exchangesequence. In this example, the standard practice of transmitting theclear-to-send signal (CTS) after a short inter-face time interval (SIFS)would be used. However, if clear channel assessment were not idle, orthe network allocation vector (NAV) was causing suppression due to anongoing frame exchange sequence, no clear-to-send signal (CTS) responsewould occur. Thus, according to these various exemplary embodiments ofthis invention, the station transmitting the request-to-send signal(RTS) would realize that if no clear-to-send signal (CTS) response isheard after a short inter-face time interval (SIFS), the station must besuppressed. At that point, the transmitting station could either retrythe request-to-send signal (RTS) or give up until a later time.

[0085] It should be appreciated that in accordance with these exemplaryembodiments, a PCF inter-face time interval (PIFS) may be used for theretry to maintain access priority on the medium, even outside of thecontention free period (CFP), and that the request-to-send (RTS) andclear-to-send (CTS) frames may also be allowed within the contentionfree period (CFP).

[0086]FIG. 8 is a flowchart illustrating a method of updating thenetwork allocation vector (NAV) in accordance with an exemplaryembodiment of this invention. As shown in FIG. 8, the process beginswith step 800, and continues to step 810, where the duration value isset. That is, in this step, the duration value is set to a value otherthan a time period for subsequent transmission to spoof obeyingstations. Control then continues to step 820.

[0087] In step 820, a signal, such as the clear-to-send (CTS) signal issent containing the set duration value. Next, in step 830, adetermination is made as to whether the receiving station address (RA)in the signal is that of the station. If the receiving station address(RA) is that of the station, control jumps to step 860, where thenetwork allocation vector (NAV) is updated. If not, the receivingstation address (RA) is not that of the station, control continues tostep 840.

[0088] In step 840, a determination is made as to whether the receivingstation address (RA) in the signal is a group address and whether thestation is not in the addressed group. If the receiving station address(RA) is a group address and the station is not in the addressed group,control jumps to step 860, where the network allocation vector (NAV) isupdated. If not, control continues to step 850.

[0089] In step 850, a determination is made as to whether the receivingstation address (RA) in the signal is a broadcast address and whetherthe station is not a legacy station. If the receiving station address(RA) is a broadcast address and the station is not in the addressedgroup, control continues to step 860, where the network allocationvector (NAV) is updated. If not, control jumps to step 870. In step 870,the process ends.

[0090]FIG. 9 is a flowchart illustrating a method of updating thenetwork allocation vector (NAV) in accordance with another exemplaryembodiment of this invention. As shown in FIG. 9, the process beginswith step 900, and continues to step 910, where the duration value isset. That is, in this step, the duration value is set to a value otherthan a time period for subsequent transmission to spoof obeyingstations. Control then continues to step 920.

[0091] In step 920, a signal, such as the request-to-send (RTS) signalis sent containing the set duration value. Next, in step 930, adetermination is made as to whether the receiving station address (RA)in the signal is a broadcast address. If the receiving station address(RA) is a broadcast address, control jumps to step 980, where thenetwork allocation vector (NAV) is updated. If not, the receivingstation address is not a broadcast address, control continues to step940.

[0092] In step 940, a determination is made as to whether the receivingstation address (RA) in the signal is a multicast address. If thereceiving station address (RA) is not a multicast address, control jumpsto step 960. If the receiving station address (RA) is a multicastaddress, control continues to step 945.

[0093] In step 945, a determination is made as to whether thetransmitting station address (TA) is a unicast address and whether thestation is not in the group identified by the multicast address. If thetransmitting station address (TA) is a unicast address and the stationis not in the group, control jumps to step 980, where the networkallocation vector (NAV) is updated. If not, control continues to step950.

[0094] In step 950, a determination is made as to whether thetransmitting station address (TA) is a multicast address and whether thestation is not in the group identified by the multicast addresscontained in the transmitting station address (TA). If the transmittingstation address (TA) is a multicast address and the station is not inthe group identified by the multicast address contained in thetransmitting station address (TA), control jumps to step 980, where thenetwork allocation vector (NAV) is updated. If not, control continues tostep 955.

[0095] In step 955, a determination is made as to whether thetransmitting station address (TA) is a broadcast address and whether thestation is not in the group identified by the multicast address. If thetransmitting station address (TA) is a broadcast address and the stationis not in the group, control jumps to step 980, where the networkallocation vector (NAV) is updated. If not, control jumps to step 990.

[0096] Next, in step 960, a determination is made as to whether thereceiving station address (RA) in the signal is a unicast address. Ifthe receiving station address (RA) is not a unicast address, controljumps to step 990. If the receiving station address (RA) is a unicastaddress, control continues to step 965.

[0097] In step 965, a determination is made as to whether thetransmitting station address (TA) is the same unicast address as thatcontained in the receiving station address (RA) and whether the stationis not in the basic service set (BSS) identified by the unicast address.If the transmitting station address (TA) is the unicast address and thestation is not in the basic service set (BSS), control jumps to step980, where the network allocation vector (NAV) is updated. If not,control continues to step 970.

[0098] In step 970, a determination is made as to whether thetransmitting station address (TA) is a multicast address and whether thestation is not in the group identified by the multicast addresscontained in the transmitting station address (TA). If the transmittingstation address (TA) is the multicast address and the station is not inthe group, control jumps to step 980, where the network allocationvector (NAV) is updated. If not, control continues to step 975.

[0099] In step 975, a determination is made as to whether thetransmitting station address (TA) is a broadcast address and whether thestation is not in the basic service set (BSS) identified by the unicastaddress. If the transmitting station address (TA) is a broadcast addressand the station is not in the basic service set (BSS), control continuesto step 980, where the network allocation vector (NAV) is updated. Ifnot, control jumps to step 990. In step 990, the process ends.

[0100]FIG. 10 is a flowchart illustrating a method of resetting thenetwork allocation vector (NAV) in accordance with another exemplaryembodiment of this invention. As shown in FIG. 10, the process beginswith step 1000, and continues to step 1010, where the CF-End message issent. In this step, the CF-End indicates a value other than the end ofthe contention free period to spoof obeying stations. Next, in step1020, a determination is made as to whether the receiving stationaddress (RA) in the message is a broadcast address. If the receivingstation address (RA) is a broadcast address, control jumps to step 1080,where the network allocation vector (NAV) is reset. If not, thereceiving station address (RA) is not a broadcast address, controlcontinues to step 1030.

[0101] In step 1030, a determination is made as to whether the receivingstation address (RA) in the signal is a multicast address. If thereceiving station address (RA) is not a multicast address, control jumpsto step 1050. If the receiving station address (RA) is a multicastaddress, control continues to step 1035.

[0102] In step 1035, a determination is made as to whether thetransmitting station address (TA) is a unicast address and whether thestation is in the group addressed by the receiving station address (RA).If the transmitting station address (TA) is a unicast address and thestation is in the group, control jumps to step 1080, where the networkallocation vector (NAV) is reset. If not, control continues to step1040.

[0103] In step 1040, a determination is made as to whether thetransmitting station address (TA) is a multicast address and whether thestation is in the group addressed by the receiving station address (RA).If the transmitting station address (TA) is a multicast address and thestation is in the group addressed by the receiving station address (RA),control jumps to step 1080, where the network allocation vector (NAV) isreset. If not, control continues to step 1045.

[0104] In step 1045, a determination is made as to whether thetransmitting station address (TA) is a broadcast address and whether thestation is not in the group addressed by the receiving station address(RA). If the transmitting station address (TA) is a broadcast addressand the station is not in the group addressed by the receiving stationaddress (RA), control jumps to step 1080, where the network allocationvector (NAV) is reset. If not, control jumps to step 1090.

[0105] Next, in step 1050, a determination is made as to whether thereceiving station address (RA) in the signal is a unicast address. Ifthe receiving station address (RA) is not a unicast address, controljumps to step 1090. If the receiving station address (RA) is a unicastaddress, control continues to step 1055.

[0106] In step 1055, a determination is made as to whether thetransmitting station address (TA) is a unicast address, whether thetransmitting station address (TA) matches the receiving station address(RA), and whether the station is in the same basic service set (BSS). Ifthe transmitting station address (TA) is a unicast address, matches thereceiving station address (RA), and the station is in the same basicservice set (BSS), control jumps to step 1080, where the networkallocation vector (NAV) is reset. If not, control continues to step1060.

[0107] In step 1060, a determination is made as to whether thetransmitting station address (TA) is another unicast address and thestation is at the receiving station address (RA). If the transmittingstation address (TA) is another unicast address and the station is atthe receiving station address (TA), control jumps to step 1080, wherethe network allocation vector (NAV) is reset. If not, control continuesto step 1065.

[0108] In step 1065, a determination is made as to whether thetransmitting station address (TA) is a multicast address and whether thestation is in the group addressed by the multicast address. If thetransmitting station address (TA) is a multicast address and the stationis in the group, control jumps to step 1080, where the networkallocation vector (NAV) is reset. If not, control continues to step1070.

[0109] In step 1070, a determination is made as to whether thetransmitting station address (TA) is a broadcast address and whether thestation is in the same basic service set (BSS) as the unicast address.If the transmitting station address (TA) is a broadcast address and thestation is in the same basic service set (BSS) as the unicast address,control continues to step 1080, where the network allocation vector(NAV) is reset. If not, control jumps to step 1090. In step 1090, theprocess ends.

[0110]FIG. 11 is a flowchart illustrating a method of sending anadditional clear-to-send (CTS) signal after a first clear-to-send (CTS)signal in accordance with an exemplary embodiment of this invention. Asshown in FIG. 11, the process begins with step 1100, and continues tostep 1110, where the duration value is set. That is, in this step, theduration value is set to a value other than a time period for subsequenttransmission to spoof obeying stations. Control then continues to step1120.

[0111]FIG. 11 is a flowchart illustrating a method of receiving anadditional clear-to-send (CTS) signal after a first clear-to-send (CTS)signal in accordance with an exemplary embodiment of this invention. Asshown in FIG. 11, the process begins with step 1100, and continues tostep 1110, where the request-to-send (RTS) signal is received by astation within range. Next, in step 1120, a determination is made as towhether the station is an obeying station. If the station is an obeyingstation, control continues to step 1130, where the network allocationvector (NAV) of the obeying station is updated. Else, the station is notan obeying station and control jumps to step 1170.

[0112] In step 1140, a timer is set. Next, in step 1150, a determinationis made as to whether the timer expired before receipt of aclear-to-send (CTS) signal. That is, a determination is made as towhether a first clear-to-send (CTS) signal or an additionalclear-to-send (CTS) signal sent by the station sending therequest-to-send (RTS) signal is received by the obeying station within apredetermined period of time.

[0113] If the timer expires before receipt of a clear-to-send signal,control continues to step 1160, where the network allocation vector(NAV) is reset. Otherwise, control jumps to step 1170. Accordingly, anadditional clear-to-send (CTS) signal sent immediately after the firstclear-to-send (CTS) signal, or otherwise immediately following therequest-to-send (RTS) signal, is sent before expiration of the timer tothe obeying station, which may have problems hearing the firstclear-to-send (CTS) signal, and may prevent the obeying station fromincorrectly resetting its network allocation vector (NAV). Control thencontinues to step 1170, where the process ends.

[0114] It should be appreciated that many other possibilities exist.That is, it should be appreciated that the exemplary embodimentsdiscussed above are just a small list of examples of how the principlesof the present invention can be applied. Other arrangements and methodscan be implemented by those skilled in the art without departing fromthe spirit and scope of the present invention. Other arrangements andmethods can be implemented by those skilled in the art without departingfrom the spirit and scope of the present invention.

What is claimed is:
 1. A method for spoofing stations while transmittingdata through a medium, the method comprising: setting a duration valueto a value other than a time period for a predetermined subsequentmessage transmission; sending a first signal containing the durationvalue, wherein at least one of the stations is an obeying station thatupdates a network allocation vector in accordance with the durationvalue if a second signal is detected after the first signal and thatresets the network allocation vector if the second signal is notdetected after the first signal; and sending a third signal containingthe duration value, wherein if the at least one station resets thenetwork allocation vector because the second signal is not detectedafter the first signal, the at least one station updates the networkallocation vector in accordance with the duration value contained in thethird signal.
 2. The method of claim 1, wherein the first signal is arequest-to-send signal and the second signal is a clear-to-send signal.3. The method of claim 2, wherein the third signal is a clear-to-sendsignal.
 4. The method of claim 1, wherein the third signal is sentimmediately after the second signal.
 5. The method of claim 1, whereinthe third signal is sent immediately after the first signal.
 6. Themethod of claim 1, wherein the obeying station is a legacy station thatdoes not practice an enhanced 802.11e standard.
 7. The method of claim1, wherein the duration value represents a time period for suppressingtransmissions by the obeying station.
 8. The method of claim 7, whereintransmissions of unknown protocols are given preferential use of themedium when the transmissions by the obeying station are suppressed. 9.The method of claim 7, wherein transmissions of hidden stations aresuppressed, and stations which would otherwise be suppressed are givenpreferential use of the medium.
 10. The method of claim 7, whereincritical transmissions are given preferential use of the medium when thetransmissions by the obeying station are suppressed.
 11. The method ofclaim 7, wherein at least some of the stations are provided in anoverlapping basic service set, and stations of the overlapping basicservice set are given preferential use of the medium when thetransmissions by the obeying station are suppressed.
 12. The method ofclaim 7, wherein stations of an enhanced version of a standard are givenpreferential use of the medium when the transmissions by the obeyingstation are suppressed.
 13. A machine-readable medium having storedthereon a plurality of executable instructions, the plurality ofinstructions comprising instructions to: set a duration value to a valueother than a time period for a predetermined subsequent messagetransmission; send a first signal containing the duration value, whereinat least one of the stations is an obeying station that updates anetwork allocation vector in accordance with the duration value if asecond signal is detected after the first signal and that resets thenetwork allocation vector if the second signal is not detected after thefirst signal; and send a third signal containing the duration value,wherein if the at least one station resets the network allocation vectorbecause the second signal is not detected after the first signal, the atleast one station updates the network allocation vector in accordancewith the duration value contained in the third signal.
 14. Themachine-readable medium of claim 13, wherein the first signal is arequest-to-send signal and the second signal is a clear-to-send signal.15. The machine-readable medium of claim 13, wherein the third signal isa clear-to-send signal.
 16. The machine-readable medium of claim 13,wherein the third signal is sent immediately after the second signal.17. The machine-readable medium of claim 13, wherein the third signal issent immediately after the first signal.
 18. The machine-readable mediumof claim 13, wherein the obeying station is a legacy station that doesnot practice an enhanced 802.11e standard.
 19. The machine-readablemedium of claim 13, wherein the duration value represents a time periodfor suppressing transmissions by the obeying station.